Fifteen years ago, Pluto was kicked out of the planet club. On August 24, 2006, members of the International Astronomical Union voted in favor of a new definition of what constitutes a planet. What was once considered the solar system’s ninth planet no longer qualified.
The public outcry was immediate. “In changing the definition of planet, the International Astronomical Union is messing with something much bigger than it is,” one Science News reader complained in a letter to the editor.
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